[propbeanie]

This would be an addition to the Patrol Objectives folder (like DarterRescue.mis & tsr in a DarterRescue folder). It doesn't have to be assigned to anybody. Just use the DynamicMiss.cfg to "link" to it. If a player is within 500km (or whatever distance you want to use) and they "phone home" with a Status Update, then they'd get assigned the mission. The mission's main Objective would be "Life Guard Duty", but it wouldn't trigger the Survivors or Life Rafts until you get within the Map Zone, which has the trigger attached, that "triggers" the "Instance Update" to "Spawn" them. That way, they're not drifting all over the ocean making for an impossible to fulfill mission. In the DynamicMiss.cfg you would add

[Section 222] ; or whatever your next number is
FileName=Data/Campaigns/Campaign/PatrolObjectives/DarterRescue/DarterRescue.mis
StartDate=19441024
EndDate=19441030
GameModes=Career
InclusionProbability=100
MinimumDifficultyRating=0
MinimumPlayerRating=-3
EntryFocalPointLong=17006484.000000 ; comes from your mission
EntryFocalPointLat=3236390.000000 ;comes from your mission
MaximumDistanceFromStartPoint=1500 ; how far away the player is from there
ExclusiveLayer=Yes
ExclusiveLayerID=302 ; sequential number set to after your last entry's number
EvaluationReason=StatusReport
AllMatch=PrimaryObjCompleted
PartialMatch=
PartialMatchingMinimumPercentage=
MinimumFuelPercentage=35
MinimumAmmoPercentage=25

You should be able to use the center mark of your Map Zone as the FocalPoint numbers. You could have a message set to go off late on the 24th and interrupt game play to inform the player of the incident, and that help is needed, and for them to please check-in with headquarters... ??